In the Orinoco Basin, in Trinidad, in North America, and in other areas, deposits of heavy oil and asphalt occur which are noted for their high bitumen content. These natural substances--which resemble oil and are commonly known as bituminous oil--can only be extracted by processes reducing viscosity and not by standard refinery methods. The extraction method currently used in the Orinoco Basin comprises emulsification of the bituminous oil at bed level, extraction of the emulsion, upgrading and transport. During the further processing stage, the saline emulsion water of the primary emulsion is replaced by river water with low salt content. This secondary emulsion can be temporarily stored and transported by pipelines or oil tankers.
Emulsifying the bituminous oils with water brings about a considerable reduction in the viscosity of these oils. The original viscosity in excess of 10000 cP at ambient temperature is reduced to the range of 400 to 1200 cP as a consequence of emulsification. It is only this viscosity-reducing process that permits the extraction, transport and further processing of bituminous oil. The water content of the emulsion is approximately 30% by weight, i.e. 70% by weight bituminous oil.
Owing to this high bitumen content, the bituminous oil cannot be processed by traditional refinery methods.
At present, the bituminous oil emulsion is used to fire power stations. The high sulphur content in bituminous oils (from 3 to 4%) causes a correspondingly high level of environmental pollution--a level which is becoming more and more unacceptable in the industrialized countries. The alternative is to produce desulphurized fuel gas by partial oxidation of bituminous oil emulsion, thus obtaining raw gas mainly consisting of CO and H.sub.2. The raw gas is subsequently treated to obtain desulphurized fuel gas suitable for firing combined cycle power plants. Jochen Keller describes the combined cycle power plant--in other words, a gas and steam turbine process with upstream partial oxidation (gasification)--in his article entitled Diversification of Feedstocks and Products: Recent Trends in the Development of Solid Fuel Gasification Using the Texaco and HTW Process published in FUEL PROCESSING TECHNOLOGY No. 24 (1990: pp247-268) by Elsevier Science Publishing B. V. Amsterdam. Said report is, however, confined to the gasification of solid fuels.
The partial oxidation of viscous fuels such as mineral oil residues from vacuum distillation units, said oxidation taking place during gasification, is already known and, consequently, gasification is feasible in a combined-cycle power station using viscous fuel. Please consult: L. Nelson & J. Brady New Opportunities for Fuel Oil in Power Generation: Heavy Residue Gasification Schemes--a paper presented at the Institute of Petroleum in London on Feb. 19, 1990.
A special kind of viscous fuel is the above-mentioned bituminous oil emulsion, the extractions nd properties of which are discussed by I. Layrisse, H. Rivas et al in Production, Treatment and Transportation of a New Fuel: Orimulsion (TM)--in a paper presented at the 12th International Conference on Slurry Technology held in New Orleans, La./USA, from Mar. 31 to Apr. 3, 1987. In addition to CO, H.sub.2, CO.sub.2 and CH.sub.4, the raw gas from the partial oxidation of the bituminous oil emulsion contains one to two percent carbon black--with reference to the oil deployed--and sulphurous ingredients such as H.sub.2 S and COS. The carbon black and the sulphurous ingredients are removed by repeated gas scrubbing whereas the purified gas is pressurized and fed as fuel to a gas turbine.
The partial oxidation of bituminous oil emulsion is also suitable for the generation of synthesis gas or hydrogen--in other words, as an intermediate process step for a wide range of chemicals such as methanol, ammonia, oxy-products, formic acid and acetic acid.
The concepts for partial oxidation of bituminous oil are based on the low viscosity of the bituminous oil emulsion which permits pumping and atomizing of the emulsion in a burner currently used for the gasification of oil.
The oil gasification burner guides the reactants--bituminous oil emulsion and oxygen--into the gasification reactor and atomizes the bituminous oil emulsion at the burner mouth due to the high gas flow velocity of the reactants. Atomization is only possible as long as the liquid feedstock possesses a viscosity which does not exceed an average of 2000-3000 cP. The high water content of the bituminous oil emulsion adversely affects the process because the water evaporates in the gasification zone and the vapor is heated to the gasification temperature of 1300.degree.-1500.degree. C. This extra heat requirement causes an additional consumption of oxygen and oil.